Morphometric analysis of shell and operculum variations in the viviparid snail, Cipangopaludina chinensis (Mollusca: Gastropoda), in Taiwan

The viviparid snail, Cipangopaludina chinensis, is one of the widely distributed freshwater gastropods in Asia, whose intraspecific variations in shell morphology and operculum were thought to be due to ontogenetic allometric growth or environmental effects. In this study, morphometric analyses were applied to discriminate shell and operculum variations in 251 individuals of C. chinensis from 5 populations, including Chutzuhu, Laumay, Lantan, and Wanda in Taiwan, and 1, Kwangju, in Korea. The allometric shell growth pattern in C. chinensis was identified using linear regression analysis. Thirteen shell and operculum characters were measured and examined using multidimensional scaling (MDS) and canonical discriminate analysis (CDA). These 2 analyses clearly demonstrated that 2 morphotypes, namely a tall-spired form and a short-spired form, exist among the 5 populations. MDS indicated that snails with the shorter shell spire in Chutzuhu and Laumay were morphologically related. CDA suggested that spire height is the most important character contributing to variation between these populations. One of the factors causing variation in spire height within and between populations is allometric growth. Different growth rates between the spire and other portions of the shell result in the shell changing shape with growth. Linear regression demonstrated that the spire of the tall-spired form lengthens at a faster rate than that of the short-spired form. Different growth rates in the spire thus contributed to the major difference in shell shape between the 2 morphotypes. Ontogenetic allometric growth and environmental factors that contribute to the configuration of the 2 morphotypes in C chinensis are discussed.